(a) Field of the Invention
The present invention relates generally to a cursor control device construction, and more particularly to a cursor control device construction which facilitates mounting of the wheels, light sources and sensors on a circuit board and which permits a spindle of the wheel to be disposed at a relatively higher position to achieve precise reading of signals and to enable the wheel to be mounted on the circuit board prior to tin soldering.
(b) Description of the Prior Art
Conventional cursor control devices may be generally classified into three main types, namely, mechanical, optical and semi-optical.
In Semi-optical cursor control devices, the construction generally includes a body containing a circuit board therein and having a hole in a bottom side thereof for mounting of a ball which may roll freely therein. The body also accommodates a couple of encoders, each including a wheel which has a spindle extending in the direction of the ball, the spindle being provided with a roller which is in a frictional relationship with the ball, such that the wheel may rotate synchronously therewith. The wheel is provided with a light source and a sensor on both sides. The light emitted by the light source is just perpendicular to the spindle, and the sensor is disposed in the proximity of the periphery of the wheel so as to receive light passing via the periphery of the wheel. When the wheel rotates, some of the light emitted by the light source will be blocked by the wheel while some will pass via the periphery thereof to reach the sensor. These two conditions may be respectively represented by 0 and 1. When the wheel performs continuous rotation (whether clockwisely or counter-clockwisely), the following four signals will be obtained: (1, 1), (0, 1), (0, 0) and (1, 0). After undergoing conversion by means of the circuit board, these signals may control a cursor to move across the screen of a display. The two encoders are provided to respectively control the cursor to move across the screen horizontally and vertically, or in any other direction.
However, since-the roller at one end of the spindle of the wheel rubs against the ball so that the ball and the wheel may synchronously rotate, the spindle has to be maintained at a certain height in order that the roller may always be in contact with the ball within a suitable extent. In other words, the wheel may have a lower rim thereof in contact with the circuit board below when mounted thereon. Therefore, the wheel cannot be mounted on the circuit board before the circuit board has undergone tin soldering since the wheel, due to its material and its position on the circuit board, may be easily damaged during the process. Besides, as the spindle of the wheel has to be maintained at a certain height, the diameter of the wheel is restricted and cannot be increased as desired. If the diameter of the wheel is prolonged, the wheel will certainly have the lower rim thereof touching the body. However as reading of signals may become more precise with the increase of the diameter of the wheel, it is imperative to find a solution to solve the above-mentioned problem.
Furthermore, the relative relationship among the wheels, light sources, and sensors will greatly affect the precision of signal reading. If these components are not properly mounted and positioned on the body of the cursor control device, signal reading will be defective or will even fail. But in the prior art, these components are individually welded to the circuit board directly so that it is necessary to adjust their position to ensure that they are properly positioned on the circuit board, which is very inconvenient and time-consumptive.